1. Field of the Invention
The present invention relates to a method of producing a nitride semiconductor light-emitting device and more particularly to a production method that can improve crystal quality of the active layer included in the light-emitting device and then light-emitting efficiency of the device.
2. Description of the Background Art
In the light-emitting device, it is important to reduce crystal defects such as dislocations in the active layer for causing light emission, in order to improve the light-emitting efficiency (refer to Japanese Patent Laying-Open Nos. 10-335757, 11-177175 and 2001-168385, for example).
In order to suppress formation of such crystal defects, in the case that a layer, such as a clad layer of a high Al concentration, having a composition different from that of quantum well layers included in an active layer of a nitride semiconductor light-emitting device is placed in proximity to the active layer, it is proposed to introduce into the clad layer a multilayer film structure varying in Al concentration.
Furthermore, in order to relax strain caused by difference between lattice constants of an n-type or p-type GaN layer and the well layers, it is also proposed to introduce into the n-type or p-type GaN layer a multilayer film structure having its In concentration gradually increased in approaching the active layer.
In the multilayer film structure, however, layers in contact with each other have compositions different from each other and crystal growth surfaces of these layers have different surface energy levels, and hence it is difficult to steeply (definitely) form the interface between the layers in the multilayer film structure.
If the layer interface in the multilayer film structure is not definite, dislocations may be generated from the layer interface, or the interface between the well layers in the active layer formed on the multilayer film structure may not be made definite.
The thickness of well layers including dislocations or loose interfaces is spatially irregular. In general, the internal quantum efficiency remarkably depends on the thickness of the well layers. In the case that the thickness of the well layers is irregular, therefore, portions having low internal quantum efficiency are dispersed in the well layers, and the internal quantum efficiency of the overall well layers is reduced. The internal quantum efficiency denotes the efficiency for forming photons due to recombination of electrons and holes which are charge carriers generated by electric current injected into the light-emitting device from the outside.